A water-soluble complex fullerene and gamma-cyclodextrin [C-60(gamma CD)(2)] mediates an electrocatalytic conversion of dinitrogen to ammonia. The EIS data obtained under the atmosphere of argon or nitrogen were analyzed. A decrease of the charge-transfer resistance in the presence of nitrogen was found and used for selection of the most efficient potential for the electrochemical nitrogen fixation. Optimization was verified by the preparative electrolysis and detection of ammonia. (c) 2007 Elsevier Ltd. All rights reserved.